The present invention is related to mechanisms for causing the needles on hypodermic syringes to penetrate the flesh and the plungers of the syringes to expel medicaments therefrom and through the needles into the flesh. While the invention is useful to physicians, paramedics, nurses or the like, it is particularly useful to patients who are required frequently to self-administer medicaments such as insulin in cases of diabetes.
Injector devices for facilitating hypodermic injections are known, both for medicament ampules that are furnished with the injector device, and for conventional hypodermic syringes that are operated by the device. In the case of injection from self-contained ampules, see, for example, U.S. Pat. Nos. 4,194,505, 4,316,463, and 4,413,991 to the present inventors, and U.S. Pat. No. 3,712,301 to Sarnoff. For injection from conventional syringes, see U.S. Pat. No. 4,494,358 to Fehlis, U.S. Pat. No. 3,702,608 to Tibbs, and U.S. Pat. No. 3,880,163 to Ritterskamp.
It is also known to provide a "tracked" injection wherein the medicament is caused to issue from the needle during movement of the needle into the patient's flesh for preventing tissue damage that would otherwise be caused by a "balloon" injection, wherein substantially all of the medicament is deposited after the needle reaches maximum penetration.
In clinical and home use applications such as for insulin injections, it is desirable to have a re-useable injector that incorporates a conventional syringe or the like for avoiding costs associated with discarding the ampule-type injectors after a single use. However, the injectors for conventional hypodermic syringes have other problems. For example, they are unreliable for accurate penetration and dosage because they are subject to operation with the syringe not properly seated in the device. Also, they are subject to inaccurate dosage due to loss of a portion of the medicament from the syringe prior to a necessary depth of needle penetration into the flesh. Moreover, they are subject to inadvertent premature actuation during attempts to engage the syringe with the injector device, consequently subjecting those nearby to possible injury.
A further problem with syringe injectors is that in case of a faulty injection, analysis of causation is clouded by the possibility of injector tampering, especially when the injector can be easily disassembled and improperly assembled by the user.
Thus there is a need for an injector device for a hypodermic syringe that reliably and safely facilitates administration of a precise medicament dosage without excessive tissue damage.